Release coatings are substances which control or eliminate the adhesion between an adhesive and a substrate surface, many of which have been prepared using silicone based materials. Curing of such silicone based liquid release coatings has been accomplished by solvent removal and thermal crosslinking, as is taught in U.S. Pat. No. 4,151,344. However the removal of solvent is not only energy intensive but also raises environmental concerns over solvent removal and recovery. To obviate this disadvantage, solvent free "100% reactive" organo polysiloxane compositions such as those taught in U.S. Pat. No. 4,057,596 have been developed. These coatings, based on platinum catalyzed hydrosilation reactions, address the issue of solvent omission but are nevertheless energy intensive. Additionally, curing temperatures are typically within the range of from 140.degree. to 160.degree. C., thus precluding their use on temperature sensitive substrates. When applied to paper at these temperatures, the release coated paper has a tendency to curl and drastically change dimensions during thermal cure as dehydration of the paper substrate takes place. UV-curable release coatings in the absence of solvent is therefore desirable, since these coatings can be cured at room temperature.
Free radical initiated systems based on thiol-ene reactions are described in U.S. Pat. No. 3,816,282. These systems, however, have an offensive mercaptan odor; moreover, thiol-ene systems are known to cure slowly and are thus commercially not attractive. Although the cationically curable epoxy and vinyloxy organo polysiloxanes described (U.S. Pat. Nos. 4,617,238 and 4,279,717) cure rapidly with UV exposure and provide excellent low or "easy" release, in practice these UV-curable release coatings have several limitations. First, while UV-curable silicone release coatings can readily provide a low energy surface for easy release, coating formulations with controllable level of release are difficult to achieve. Attempts to counter this with control release additives have been only partially successful in developing moderate release properties. Secondly, many potential consumers object to silicone based products because of potential contamination of conventional components in coating lines. Specifically, silicones can cause adhesion and wetting problems when present as a contaminant in protective coating resins. Also, the UV curing of silicone-based release agents exhibit a strong substrate dependence. Finally, silicones are fairly expensive and their compositions are less economically attractive than other organic resins.
An example of a UV-curable non-silicone release coating has been reported (U.S. Pat. No. 4,319,974) which employs mixtures of C.sub.(8-28) alpha olefin oxides. These are reported to be useful in paper release applications. However, the cationic polymerization of alpha olefin oxides is much slower than UV-curable silicones.
Accordingly, it is an object of this invention to obviate the above problems and to provide a rapidly curable release composition which is economically prepared and used as a release coating.
Another object of this invention is to provide a release coating composition which can be adapted to possess easy, moderate, or strong release properties.
Still another object is to provide a release coating which may be applied to a wide variety of substrates and can be rapidly cured at about room temperature.
Yet another object is to provide a silicone free release coating composition.
These and other objects of the invention will become apparent from the following description and disclosure.